In a long-term evolution (LTE) system, a user equipment (UE) receives downlink data transmitted by a base station, decodes the downlink data, obtains a response signal of the downlink data according to the result of decoding, and transmits uplink control information containing the response signal on a physical uplink control channel (PUCCH), so that the base station judges whether the data transmission is correct or wrong according to the uplink control information and hence judges whether data retransmission is needed. Wherein, the uplink control information comprises response signals for uplink data, such as acknowledgement (ACK)/negative acknowledgement (NACK)/discontinuous transmission (DTX), and channel state information (CSI), etc., wherein the ACK denotes that the data are correctly received, NACK denotes that the data are wrongly received, and DTX denotes that the UE receives no downlink control data, that is, receives no control signaling for scheduling downlink data transmission.
The response signals transmitted in the PUCCH correspond respectively to a physical channel resource, a time domain sequence and a frequency domain sequence.
FIG. 1 is a schematic diagram of resource assignment in a carrier aggregation (CA) system. As shown in FIG. 1, for a primary components carrier (PCC), such three resources are all associated with a first control channel element (CCE) of a physical downlink control channel (PDCCH) for scheduling the downlink data and to which the response signals correspond. And for a secondary components carrier (SCC), the PUCCH resources are explicitly indicated by ACK_NACK resource indicators (ARIs) in the PDCCH.
Wherein, a base station (BS) transmits a list of usable PUCCH to a UE via a radio resource control (RRC) protocol, the list comprising corresponding relations between states indicated by the ARIs and the PUCCH resources. For example, several PUCCH resources may be included, such as {PUCCH0, PUCCH1, PUCCH2, PUCCH3}, where, ARI=01 corresponds to resource PUCCH1, and ARI=11 corresponds to resource PUCCH3. In this way, the UE may select corresponding PUCCH resources according to the values of the ARIs. For example, when ARI=01, PUCCH1 is selected, and when ARI=11, PUCCH3 is selected. Wherein, as PDCCH in an SCC contains 2 bits of ARI, the 2 bits can only indicate four states, and it is impossible to select one PUCCH among N PUCCHs prepared for explicit allocation.
For an time division duplex (TDD) system of LTE system (LTE TDD system), in many cases, an uplink (UL) subframe corresponds to multiple downlink (DL) subframes, that is, for any UE in the system, an uplink subframe needs to transmit values of response signals of multiple downlink subframes corresponding to the uplink subframe.
FIG. 2 is a schematic diagram of the available configuration manner in an LTE TDD system. As shown in FIG. 2, the number of the downlink subframes is different from that of the uplink subframes in one frame. Taking configuration2 as an example, there exist 8 downlink subframes (since uplink control information cannot be transmitted in S, S is deemed as a downlink) and 2 uplink subframes, each of the uplink subframes being responsible for feedback of response signals (ACK/NACK) of 4 downlink subframes.
For a CA TDD system, at most 5 uplink CCs and 5 downlink CCs may be used, and if configuration2 shown in FIG. 2 is used and each of the uplink subframes is responsible for 4 downlink subframes, then each uplink CC needs to feed back the ACK/NACK of at most 5 downlink CCs, that is, the ACK/NACK of total 40 physical downlink shared channels (PDSCHs) (if a CC transmits two code words in a subframe, two ACK/NACK bits are needed, that is, 2×5×4=40). In an uplink, it is substantially impossible to feed back all these bits.
At present, the above problem may be solved by an ACK/NACK bundling. FIG. 3A is a schematic diagram of the full bundling used in a CA TDD system, and FIG. 3B is a schematic diagram of the time domain bundling used in a CA TDD system.
As shown in FIGS. 3A and 3B, downlink assignment indicators (DAIs) exist in a PDCCH, and there are two potential counting functions:
1) accumulated at current moment number of PDCCHs that have been transmitted at the BS side. For example, when the BS transmits a first PDCCH, 0 is tagged on the first PDCCH, and when a second PDCCH is transmitted, 1 is tagged on the second PDCCH, and so on. If the UE detects PDCCH0 and PDCCH2 successfully, according to the tag on the PDCCHs, it may be known that PDCCH1 is missed. And although the detected downlink data are all ACK, but the UE feeds back NACK since it knows that one PDCCH is missed in detection.
2) the total number of transmitted PDCCHs is recorded.
As shown in FIG. 3A, in full bundling, the DAI values are accumulatively counted taking CC first and then subframe into consideration; and as shown in FIG. 3B, in time domain bundling, the DAIs are effective in each subframe in a CC, and an accumulated number is counted.
As shown in FIGS. 3A and 3B, manners of PUCCH resource allocation on PCC and SCC are as follows:                in the PCC, resources are implicitly mapped, and in this way, the PUCCHs to which each subframe in the PCC corresponds are different; in the SCC, resources are explicitly mapped, and in this way, the PUCCHs to which each subframe in the SCC corresponds may be different, and may also be identical, depending on whether the ARIs are identical or not. For the time domain bundling, identical resources may be allocated, such as PUCCH2 shown in FIG. 3B. Hence, uplink PUCCH resources may be saved when the time domain bundling is used.        
In the full bundling manner shown in FIG. 3A, the UE detects the downlink data received from the PCC and SCC and obtains detection results (ACK/NACK), performs an AND operation on all the detection results, and then transmits the results (ACK/NACK) after the AND operation on the PUCCH to which the last received PDCCH corresponds.
In the time domain bundling manner shown in FIG. 3B, the UE performs an AND operation on the detection result (ACK/NACK) of each subframe in the same CC, and then feeds back the bundled results to the BS by using channel selection.
In the implementation of the present invention, the inventors found that following problems need to be solved in bundling:                1) the problem of missed detection of a downlink data which is not the last one: at present, the missed detection may be found by using DAIs; and        2) the problem of missed detection of the last downlink data: at present, whether the last downlink data is missed in detection is checked by feeding back ACK/NACK in the PUCCH to which the last received PDCCH corresponds.        
The problem of missed detection in full bundling is illustrated below with reference to FIGS. 4 and 5.
Example 1: as shown in FIG. 4, on the PCC, the BS transmits 3 PDSCHs, the UE detects one PDSCH (DAI=0, PUCCH0), and the detection result is correct (feed back ACK). And on the SCC, the BS transmits 2 PDSCHs, the UE detects two PDSCHs (DAI=2, PUCCH2; DAI=3, PUCCH3), and the detection result is correct (feed back ACK).
In full bundling, the UE receives the PDCCHs with DAI numbers 0 and 2, but does not receive a PDCCH with a DAI number 1. Hence, the UE may know that missed detection occurs and feed back NACK on PUCCH3 to which the last received PDCCH corresponds, and the BS retransmits all the data after receiving the NACK.
Example 2: as shown in FIG. 5, on the PCC, the BS transmits 3 PDSCHs, the UE detects two PDSCHs respectively corresponding to DAI=0, PUCCH0 and DAI=1, PUCCH1, and the detection result is correct (feed back ACK). And on the SCC, the BS transmits 2 PDSCHs, the UE detects two PDSCHs respectively corresponding to DAI=2, PUCCH2 and DAI=3, PUCCH3, and the detection result is correct (feed back ACK).
In full bundling, since no case of skip of DAI numbers is found, the UE does not know that missed detection occurs in the last transmitted PDSCH, and feeds back ACK on the PUCCH3 to which the last received PDCCH corresponds, and the BS detects the ACK on the PUCCH3, knows that missed detection occurs in the last PDCCH (DAI=4, PUCCH4), and retransmits the last PDSCH.
It can be seen from above that the missed detection of the last PDCCH induces the following problems:                1) if the UE does not feed back ACK/NACK on the PUCCH to which the last received PDCCH corresponds, the BS is unable to know whether the UE receives all the PDCCHs and all the PDCCHs are correctly received, or the last PDCCH is missed in detection and the former 4 PDCCHs are correctly received;        2) in full bundling, the problem of 1) is well solved by feeding back ACK/NACK on the PUCCH to which the last received PDCCH corresponds; however, in the time domain bundling, such a problem still exists.        
FIG. 6 is a schematic diagram showing the occurrence of missed detection in time domain bundling.
As shown in FIG. 6, the bundling result obtained by the UE is (ACK, ACK), and if one QPSK symbol is used to denote an (ACK, ACK) state and a PUCCH to which the last PDCCH detected in the SCC detection corresponds is used in feedback, the BS may know that the last PDCCH in the SCC is missed in detection, but is unable to know whether all the PDCCHs in the PCC are detected and all the PDCCHs are correctly received, or the last PDCCH is missed in detection and all the detected PDCCHs are correctly received. On the contrary, if the PUCCH to which the last detected PDCCH in the PCC corresponds is used, the same problem will occur in the SCC.
In summary, in the implementation of the present invention, the inventors found that following defect exists in the bundling technology of the prior art: in a CA TDD system, in the full bundling, many correctly received data are retransmitted, as shown in FIG. 4; and in the time domain bundling, there is no way to solve the problem of missed detection of the last PDCCH till now.